Case Report Adrenal rest tumor of the liver: A case report with immunohistochemical investigation of steroidogenesis
Kazumori Arai,1 Hiroyuki Muro,1 Makoto Suzuki,1 Noriyuki Oba,2 Kazuki Ito3 and Hironobu Sasano4
Departments of 1 Pathology,2 Surgery, 3Gastroenterology, Shizuoka General Hospital, Shizuoka and4Department of Pathology, Tohoku University School of Medicine, Sendai, Japan
A case of adrenal rest tumor arising in the liver of a 62-year- old male with chronic hepatitis type C is reported. The tumor was clinically non-functioning and required distinction from hepatocellular carcinoma. The yellowish-brown tumor mea- sured 25 x 18 x 15 mm and was located in the subcapsular portion of the right hepatic lobe. Histologically, the tumor presented features similar to those of the adrenal cortex and was predominantly composed of pale cells. Electron micrograph revealed lipid droplets and mitochondria with tubulo-vesicular cristae, consistent with the characteristics of steroid-producing cells. Immunohistochemically, the tumor expressed the adrenal 4 binding protein and a number of enzymes involved in the synthesis of adrenocor- tical steroids. At surgery, the right adrenal gland was present independently from the liver. This hepatic tumor was considered to be an adrenal rest tumor with steroido- genic capability.
Key words: adrenal rest tumor, immunohistochemistry, liver, pathology, steroidogenesis
The adrenal rest tumor, a tumor of adrenocortical cells, rarely occurs in the liver.1-5 This tumor is considered to arise from an adrenal rest, which is derived from the aberrant adrenal pri- mordium,1-10 with most of the tumors being benign.1,2,11 Adrenal rest is a minute lesion5 with a diameter of less than 7 mm, and is incidentally detected at surgery or autopsy in various sites except for the limbs.2,5,7 The frequency of the rest is high in the celiac axis, testis and broad ligament which are related to the embryogenic development of the adrenal gland.2,5-8 However, adrenal rest tumor is uncommon even in those sites.5-9 In the liver, in which even the adrenal rest is seldom detected,2,5 the tumor is very rare.
On pathological diagnosis, it is difficult to distinguish the adrenal rest tumor from hepatocellular adenoma and hepato-
cellular carcinoma due to morphological similarity.1-4,12 Although proof of the content or excretion of adrenocortical hormones by the tumor cells is required for diagnosis, 1,3 demonstration of these functions using paraffin-embedded tissue sections is impossible. Recently, it has become immunohistochemically possible to detect protein antigens involved in adrenocortical steroidogenesis, and the steroido- genic capability of the adrenal rest tumor has been shown in the spinal nerve root and broad ligament.9,10 We investigated these antigens in a non-functioning adrenal rest tumor of the liver, and then demonstrated the steroidogenic capability of the hepatic tumor.
CLINICAL SUMMARY
A 62-year-old male, followed up since 1984 because of his history of chronic hepatitis type C virus (HCV). In March 1994, a solid mass, which measured 22 mm in dimension, was detected in the postero-superior subsegment of the right hepatic lobe by ultrasonography. Computed tomography showed that the mass was heterogeneous with low density (Fig. 1). Angiography revealed that the mass was nourished by the hepatic artery and presented as a hypervascular image (Fig. 2). There were no marked abnormalities in the routine laboratory investigations except for anti-HCV anti- body positivity. The levels of the tumor markers such as alpha-fetoprotein (AFP), carcinoembryonic antigen and protein-induced vitamin K absence or antagonism II were within normal limits. Furthermore, only cirrhotic liver tissue was detected on subsequent liver biopsy. Based on the above findings, hepatic angiomyolipoma was primarily sus- pected, but other malignant tumors were not ruled out com- pletely. The patient underwent subsegmental resection of the right hepatic lobe in February 1996. During operation, the right adrenal gland was recognized as being independent from the liver, and showed neither atrophy nor swelling. Because of the lack of any symptoms of hormonal abnormal-
Correspondence: Kazumori Arai, MD, Department of Pathology, Shizuoka General Hospital, 4-27-1 Kitaando, Shizuoka 420-0881, Japan.
ity, blood and urinary hormone levels were not measured. The postoperative course was uneventful 3 years postopera- tively and there was no sign of recurrence of the tumor.
PATHOLOGICAL FINDINGS
The pathological specimen was fixed in 10% formalin and routinely processed for light microscopy. Using a Histofine Kit (Nichirei Co. Ltd, Tokyo, Japan), the tissue sections were immunostained with the antibodies listed in Table 1 by the peroxidase-labeled streptoavidin-biotin amplified method. The tissue sections for Ki-67 immunostain were treated with both 0.2% trypsin and microwaved in 0.01 mol/L citrate buffer (pH 6.0) for antigen retrieval.
| Antigen | Antibody | Source | Ref. | |
|---|---|---|---|---|
| Cytokeratin | mAb KL-1 | Immunotech | ||
| Epithelial membrane antigen | mAb E29 | DAKOŤ | ||
| Vimentin | mAb V9 | DAKOŤ | ||
| Alpha-fetoprotein | mAb ZSA06 | Nichirei | ||
| Ki-67 antigen | mAb MIB-1 | Immunotech | ||
| S-100 protein | Rabbit polyAb | Nichirei | ||
| Chromogranin A | Rabbit polyAb | DAKO* | ||
| P450scc | Rabbit polyAb | Sasano H | 13 | |
| 3ß-HSD | Rabbit polyAb | Sasano H | 14 | |
| P450C21 | Rabbit polyAb | Sasano H | 15 | |
| P450C17 | Rabbit polyAb | Sasano H | 16 | |
| P450C11 | mAb | Sasano H | 17 | |
| DHEA-ST | Rabbit polyAb | Sasano H | 18 | |
| Ad4BP | Rabbit polyAb | Sasano H | 19, | 20, 21 |
P450scc, cholesterol side chain cleavage; 3ß-HSD, 3ß-hydroxy- steroid dehydrogenase; P450C21, 21-hydroxylase; P450C17, 17a-hydroxy- lase; DHEA-ST, dehydroepiandrosterone sulfotransferase; P450C11, 11ß-hydroxylase; Ad4BP, adrenal 4 binding protein; polyAb; polyclonal antibody. Sources: Immunotech, marseille, France; +DAKO, Carpinteria, CA, USA; Nichirei, Tokyo, Japan; * DAKO, Glostrup, Denmark.
Electron microscopic examination was performed on 10% formalin-fixed tissue, following postfixation in 2% osmium tetroxide, embedded in epoxy resin, and then stained with uranyl acetate and lead citrate.
PATHOLOGICAL FINDINGS
Macroscopic findings
A single subcapsular tumor was observed in the micronodu- lar cirrhotic liver. The yellowish-brown tumor, measuring 25 x 18 x 15 mm, was well circumscribed and showed hemor- rhagic necrosis in the center (Fig. 3).
Light microscopic findings
The tumor was predominantly composed of pale cells, and the clusters of eosinophilic cells were partially observed near the center of the tumor. These tumor cells were aligned in alveolar or fascicular arrangements, in a similar manner with the features of the adrenocortical tissue (Fig. 4a). The major- ity of the nuclei of these cells were ovoid or somewhat irregu- lar. There was no evidence of mitotic activity. The tumor was surrounded by a thin fibrous capsule, which was partially lacked in some areas (Fig. 4b). In the frozen sections, the tumor cells were positively stained for lipid with Sudan III. Production of bile, periodic acid-Schiff-positive materials and argyrophilic granules were not observed in the tumor cells. Adrenal medulla was not found in the tumor.
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Immunohistochemistry
The tumor cells did not stain for epithelial markers such as cytokeratin and epithelial membrane antigen, vimentin, S- 100 protein, chromogranin A and AFP, as shown in the previ- ous report.10 In contrast, positive staining for adrenal 4 binding protein (Ad4BP) and the six types of steroidogenic enzymes (Table 1) was detected in those cells (Figs 5,6). The staining intensities for the steroidogenic enzymes varied irregularly among the cells, but the positivity for Ad4BP was evenly detected in the nuclei of the tumor cells.
The number of Ki-67-positive tumor cells per 100 cells was found to be 1.80 ±0.98 through evaluating 10 different fields.
Electron microscopic findings
The tumor cells featured abundant lipid droplets and well- developed mitochondria. The majority of mitochondria were roundly swollen and contained tubulo-vesicular cristae, resembling those of the adrenocortical cells (Fig. 7).
DISCUSSION
The tumor showed light- and electron-microscopic features very similar to those of the adrenal cortex.22 The tumor cells immunohistochemically expressed the Ad4BP and steroido-
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genic enzymes which denote the important indices on steroid-producing cells.9,10,13-21,23 Ad4BP is a universal regulator of steroidogenic P450 gene transcription and is almost constantly expressed not only in the normal condition but also in such biologically altered conditions as hyperplasia or neoplasm, including non-functioning lesions.19-21 However, Ad4BP can also be detected in the gonads, brain and pla- centa, so that the expression is not specific to the adrenal cortex.21 In contrast, the types of steroidogenic enzymes can differ between organs and hormones.6,13-18,23 17o .- Hydroxylase (P450C17) is involved in the synthesis of gluco- corticoid and sex hormones, and is distributed only in the adrenal cortex and gonads.16 21-Hydroxylase (P450C21), 11ß- hydroxylase (P450c11) and dehydroepiandrosterone sulfo- transferase (DHEA-ST) are expressed in the adrenal cortex but not in the gonads.6,15,17,18 Therefore, the present case, expressing all six types of steroidogenic enzymes, was
thought to differentiate functionally into the adrenal cortex.6,13-21,23
To our knowledge, there have been five case reports in which steroidogenesis by adrenal rest tumor has been inves- tigated. Two of these cases were functioning adrenal rest tumors of the liver which caused virilization or Cushing’s syndrome.3,4 In the first case, cortisol and testosterone were immunohistochemically detected in the tumor cells.3 However, using immunohistochemistry for detection of steroid hormones, it is difficult to recognize specifically the steroid-producing cells.24 The second case indicated the steroidogenic capability in vitro by radioimmunoassay but no steroids were demonstrated by chromatography.4 The other three cases were clinically non-functioning, and showed the expressions of Ad4BP and steroidogenic enzymes.9,10 The same findings were also obtained in the present case, and consequently considered the tumor to have a steroidogenic capability similar to that of the adrenal rest tumor in the other sites.9,10
Adrenal rest tumor in the liver is a well-circumscribed, yel- lowish, nodular lesion which chiefly occurs under the capsule of the right hepatic lobe,1 and is thought to be nourished by the hepatic artery,3,4 as shown in the present case. Histologi- cally, the tumor was composed of pale and eosinophilic cells.1,2,4 Important lesions in the differential diagnosis of the tumor were: hepatocellular adenoma; hepatocellular carci- noma; metastatic renal cell carcinoma; and metastatic adrenocortical carcinoma.1-3,12 The tumor cells in some hepa- tocellular adenomas and hepatocellular carcinomas are morphologically similar to adrenocortical cells1,12 with some of these tumors producing the adrenocorticotropin or corticotropin-releasing factor, inducing secondary hypercorti- calism. 12,25 Therefore, in the diagnosis of adrenal rest tumor in the liver, it is necessary to objectively demonstrate the differ- entiation to the adrenal cortex. Accordingly, immunohisto- chemistry for protein antigens related to adrenocortical steroidogenesis constitutes the most significant method in the differential diagnosis.17,20 This immunohistochemical
method is also useful for its distinction from metastatic renal cell carcinoma.18,20 To distinguish it from metastatic adreno- cortical carcinoma, identification of the intact adrenal gland is necessary.1
Malignant transformation of adrenal rest tumor rarely occurs.1,11 Although the present case was accompanied by the tumor necrosis, the pathological features did not meet the histopathological criteria of adrenocortical malignancy;26 that is, high nuclear atypia, mitotic activity, atypical mitoses, eosinophilic tumor cell cytoplasm, diffuse growth pattern, vascular invasion and capsular invasion. The Ki-67 labeling index is also considered useful for the distinction of malignant and benign adrenocortical tumors, and this labeling index of the present case was considerably lower than that of adreno- cortical carcinoma.27 Therefore, we considered this tumor to be benign.9,26,27
In summary, in diagnosing the adrenal rest tumor, it is important not only to ascertain morphological characteristics but also to demonstrate the steroidogenic capability of the tumor. Although the tumor of the present case was clinically non-functioning, it showed immunohistochemically the expressions of the Ad4BP and enzymes involved in adreno- cortical steroid synthesis which denote the differentiation into the adrenal cortex. To our knowledge, this is the first case of adrenal rest tumor in the liver demonstrating the expression of these proteins.
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